1. Field of the Invention
This invention relates to a cryosurgical probe and method for treating cancer by cryosurgically destroying the cancer cells. The probe is surrounded by a thermally insulating and/or heated sheath having particular dimensions so as to produce an ice ball having a corresponding size and shape that are tailored to the size, shape and location of the cancerous tissue.
2. Background Art
Cryosurgical devices have been known for use in destroying cancerous cells in a localized tissue area of a patient undergoing treatment. Early cryosurgical devices used gases or liquid nitrogen to generate extremely low temperatures to kill cancerous cells. The gaseous system typically relied on the Jewel-Thompson principal to produce a cryogenic effect, and the liquid system was based directly upon the thermal characteristics of the liquid nitrogen. Such early devices were used solely for the surface treatment of pathologic lesions but not to penetrate human tissue. These early devices are characterized by relatively low pressure (e.g. about 6 psi) and interchangeable tips to provide a desired result. Consequently, the early cryosurgical devices had limited cryogenic capacity and correspondingly limited application.
More recent cryosurgical devices are either of higher pressure (e.g. about 80 psi) liquid nitrogen systems or high pressure (e.g. 2,800 psi) argon gas systems. Such devices are typically characterized by a closed end probe in which the cryogen circulates to the probe tip. The probe tips are adapted to penetrate the patient's tissue (e.g. the prostate, liver, breast and brain) in which the cancerous cells reside. However, these recent cryosurgical probes cannot be easily modified to accept tip changes without significantly effecting the probe performance. Likewise, the cost to redesign a probe to accept different tips is expensive and often leads to operating characteristics that may not be suitable for all applications (i.e. the cryogenic effect could be severely compromised).
For example, a significant problem that is faced in prostate surgery is that the size and shape of the prostate gland varies from one patient to the next. If the ice ball that is generated by the cryogenic effect is too long, there is the risk that the neighboring sphincter will also be frozen resulting in the possibility of incontinence. If the patient's prostate is cylindrical rather than ellipsoid, the ice ball may not adequately conform to the prostate shape, whereby to introduce a risk of incomplete freezing of the cancerous cells in the prostate gland or freezing beyond the prostate and into the bladder or rectum resulting in the possibility of a urethral-rectal fistula. What is more, the round and/or tear drop shaped ice ball that is usually produced by the conventional cryoprobe does not fit well within the generally tubular seminal vesicle that is attached to the prostate which may lead to an unsuccessful procedure or other complications.
Therefore, what is needed is a cryosurgical probe that is quickly, easily and inexpensively adapted to vary the size and shape of an ice ball during cryosurgery depending upon the location and type of tissue to be treated so as to confine the cryogenic effect to a localized cancerous area and thereby avoid the risks that are associated with conventional cryoprobes.